Wide area trunked radio communication systems are well known. Such systems typically include remote, transmitter sites, e.g., repeaters, which serve a number of subscriber units, or radios, in the system. Subscriber units may be portable radios, mobile radios, consoles, or radiotelephones.
Typically, trunked radio system sizes range from two repeaters per site, to 20 repeaters per site. In a system having 20 repeaters, 19 of these repeaters may be dedicated voice/data (hereinafter "voice") channels while one repeater is a dedicated control channel which transmits/receives control signals to/from radios in the system. Some systems employ all available channels as voice channels; the control function for these systems is typically accomplished using either a hard-wired network connecting the repeaters, or with non-audible control signalling on some of the voice channels. In either case, the control traffic reduces the efficiency of a system, the primary purpose of which is to provide voice communications among its subscriber units.
As a first example of the problem, consider a small, low density system 100 (in FIG. 1A) having two voice channels (104, 106) and one control channel (102). When the number of users is relatively small (e.g., 100-300), two active voice channels are sufficient to maintain an acceptable level of service to the users. As the number of active subscriber units grows, however, the need may arise to add voice channel capability to the system. Adding another voice channel to such a small system will likely be a cost prohibitive solution to the problem. Because of this, users must live with the reduced system efficiency until they can afford to add another repeater for voice communications.
As a second example, consider a large, high density system having many voice channels and one control channel, such as system 150 shown in FIG. 1B. When the number of users is relatively small for such a multi-channel system (e.g., 3000-5000), one control channel is sufficient to maintain an acceptable level of service to the users. As the number of active subscriber units grows, however, the need may arise to add control channel capability to the system. Adding another permanent control channel to serve a temporary increase in the number of users, like the small system example, represents a cost prohibitive solution to the problem. Therefore, users must live with the reduced system efficiency until the addition of a another dedicated control channel can be cost-justified.
Accordingly, there exists a need for a trunked radio system which provides temporary voice or control channel capability, as required, by using existing hardware. Such a system should allow dynamic allocation between control and communication resources, while providing an acceptable level of communication service to the subscriber units in the system.